TBPA stands for which of the following in the context of thyroxine transport?

• A. Thyroxine-Binding Prealbumin
• B. Transthyretin Binding Protein
• C. Thyroxine-Binding Albumin Carrier
• D. Thyroid-Binding Plasma Antigen

Answer: (A)

Thyroxine is carried in the blood by several binding proteins, among which transthyretin (historically called prealbumin) plays a notable role in transporting thyroxine. The term TBPA stands for Thyroxine-Binding Prealbumin, which is just another name for transthyretin. This protein binds thyroxine and helps shuttle it through circulation, often together with retinol-binding protein. Among the given options, this expansion is the correct one because it directly reflects the historical and widely recognized name for the thyroxine-binding carrier associated with transthyretin. The other choices do not correspond to standard names used for thyroxine transport proteins.